CINCINNATI — Left-hander J.A. Happ joined the Pittsburgh Pirates on Saturday and threw in the bullpen, getting ready to join a rotation that'll need him for at least a few weeks.

The Pirates optioned left-hander Bobby LaFromboise back to Triple-A Indianapolis on Saturday to open a roster spot for Happ, who was acquired from Seattle in a trade the previous day. The 32-year-old starter arrived from Minnesota, where the Mariners are playing over the weekend.

"I had no idea, so I was surprised," Happ said. "I'm happy to be here. It's an exciting time here. You see them build and build and build over the years, and now everyone sees where they're at."

Happ will start next week in place of A.J. Burnett, who is on the 15-day disabled list with inflammation in his pitching elbow. Happ went 4-6 with a 4.64 ERA in 20 starts and one relief appearance for Seattle this season.

He started the season well, going 2-1 with a 2.30 ERA in his first four starts. He went 1-1 with a 7.43 ERA in six appearances in July.

"I had a few rough outings," he said. "For me, getting a fresh start would be a good thing. I know what I'm capable of, and I'm healthy."

Happ has played for Philadelphia, Houston, Toronto, Seattle and now Pittsburgh. He's a .089 career hitter with two doubles, a homer and six RBIs. He was 0 for 1 with a walk in interleague play this season.

"I definitely have to find some of my bats here again," he said.

LaFromboise was called up Friday and didn't appear in a 5-4 win over the Reds on Friday night. He was called up one time previously this season and threw a scoreless inning at Philadelphia on May 14.